Go mad in hospital department building in need of oxygen (7)
I believe the answer is:
enthuse
'go mad' is the definition.
'hospital department building in need of oxygen' is the wordplay.
'hospital department' becomes 'ent'.
'building' becomes 'house' (I've seen this before).
'in need of' suggests deleting specific letters.
'oxygen' becomes 'o' (atomic symbol for oxygen).
'house' with 'o' taken away is 'huse'.
'ent'+'huse'='ENTHUSE'
'in' is the link.
(Other definitions for enthuse that I've seen before include "Gush in praise" , "Get passionate" , "Express keen interest" , "Show lively interest and keenness" , "Rave" .)